Activists say Syrian troops are shelling restive suburbs of Damascus and rebel-held areas in the central city of Homs, AP reported.

The Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees did not have any details of casualties caused by Wednesday's bombardment in Homs city and the suburb Douma.

The rural district of Houla, where 108 people were massacred last week, is in the province of Homs.

Western nations have expelled Syrian diplomats in a coordinated move to protest the massacre, which survivors say was largely carried out by pro-regime gunmen.

The Syrian government has said it will conclude on Wednesday, May 30 its own investigation into the killings. It is not clear whether the results will be made public.